The present invention relates to systems for mounting equipment on racks, and in particular to the mounting of telecommunications equipment shelves or sub-racks on rack systems.
Telecommunications equipment such as switching circuits on cards are typically held in parallel slots within shelves or sub-racks. These shelves are in turn mounted within rack structures by mounting bolts or similar connectors.
My earlier U.S. Pat. No. 5,975,315 (the entire contents of which are incorporated herein by reference) describes an equipment rack of this type for holding telecommunications equipment within shelves mounted in the equipment rack.
The rack of U.S. Pat. No. 5,975,315 comprises a base member, a pair of parallel side members extending vertically upwards from the base member and a top member coupling the free ends of the side members. Means are provided for securing the base member to a floor (or other support surface).
Rack systems such as those of U.S. Pat. No. 5,975,315 are required to conform to industry standards such as the standard xe2x80x9cETS 300-Pt3: Engineering Requirements for Miscellaneous Racks and Cabinetsxe2x80x9d set by the European Telecommunications Standards Institute (ETSI), or the xe2x80x9c23 inchxe2x80x9d standard (xe2x80x9cANSI/EIA-310-D-1992: Cabinets, Racks, Panels, and Associated Equipmentxe2x80x9d set by the American National Standards Institute and the Electronic Industries Association). In an ETSI rack conforming to ETS 300 a plurality of mounting holes are provided down the front surfaces of the two side members.
The shelves are provided with mounting means such as a pair of L-shaped brackets affixed to the front part of the sidewalls of the shelves and extending outwards from the front surface of the shelves on either side. In this way, when a shelf is inserted into the rack between the side members, a portion of the L shaped bracket overlaps the mounting holes of the respective side member, allowing a bolt or screw to affix the bracket (and thus the shelf) to the rack.
The L-shaped brackets serve a further purpose in earthing the shelves and the equipment in the shelves, by making a good electrical connection between the shelf housing and the rack structure which is itself earthed.
In a rack conforming to the 23 inch EIA standard the mounting method is similar but the support is located more deeply within the rack, i.e. at a point between the front and back of the shelves.
The susceptibility of a geographical location to severe earthquake damage is classified, with any given location being rated from Zone 1 to Zone 4 (with Zone 4 denoting the greatest risk). In Zone 4 locations, telecommunications equipment contained in standard rack systems is likely to suffer vibration- or shock-induced damage due to the potential severity of an earthquake in such a zone.
The rack of U.S. Pat. No. 5,975,315 addresses earthquake induced vibrations by providing a number of bolts for mounting the base member to the floor. When these bolts are overtightened or overtorqued (as they are designed to be), the base member is pre-stressed, and this stress is transmitted to the side members. This has the effect of increasing the frequency response of the rack. Since earthquake induced vibrations are typically low frequency vibrations (e.g. most of the energy is at frequencies of not more than about 10 Hz), many of the effects of earthquake induced vibration can be greatly reduced by this method.
Other methods of earthquake proofing telecommunications equipment racks have been proposed such as in U.S. Pat. No. 5,004,107, which discloses a rack having a heavily reinforced base portion which braces the rack against applied forces. The disadvantage of this is that the box-like base portion is bulky and limits the volume of equipment which can be housed in the rack. Since racks will typically have standard outer dimensions (e.g. 2200 mmxc3x97600 mmxc3x97300 mm for an ETSI rack), a reduction in available volume will result in more racks being needed to house the same amount of equipment, which is a severe problem in installations where space is at a premium.
In order to be certified for Zone 4 earthquake resistance, telecommunications equipment is required to undergo a vibration test which involves vibrational accelerations of up to 5 g. The equipment, which could, in use, be carrying emergency traffic, such as 911 calls, must be operational after the test is conducted without manual resetting or adjustment (so that in an earthquake scenario it would not require an operator to enter a potentially dangerous building to reset or repair the equipment.
It is therefore an object of the present invention to provide an improved method of mounting telecommunications equipment, and in particular to provide a rack and a shelf providing greater earthquake resistance to telecommunications equipment stored therein.
Due to the large amount of telecommunications equipment already deployed in rack structures, it is a further object of the invention to provide improved earthquake resistance, and preferably Zone 4 compliance, to existing racks and shelves which can be easily retrofitted in current installations with minimal modification of the shelves. Because existing shelves have been certified for structural strength and EM shielding, any significant modifications to shelf structure will require the modified design to be reassessed.
The invention provides a mounting bracket for mounting an equipment housing to a rack. The mounting bracket has a bracket body for rigid attachment to the housing, a fastener for rigid attachment to the rack, and a damping member coupling the fastener and the bracket body.
The damping member isolates the housing and bracket body from the rack and fastener, so that vibrations carried by the housing can only be transmitted to the housing via the damping member.
The conventional way of increasing earthquake resistance for telecommunications racks is to overengineer the rack structure itself and thereby prevent damage to the rack and preventing the equipment from e.g. breaking loose. The present invention takes a different approach by recognising that not all vibrations can be eliminated from the rack, even when the resonant frequency of the rack is increased it thus provides a bracket which isolates the loaded rack into a number of distinct sub-systems, each mechanically connected only via damping members.
The damping member is preferably an elastomeric material such as a silicone. Particularly preferred is very high density silicone, having a modulus of 10-15 daN/cm2. 
In the preferred embodiment, the bracket body is in the form of a plate which engages with a side panel of the housing, extending from the front to the rear. A flange which is perpendicular to the plate and depends from the front edge carries the damping member.
Such a bracket is particularly suited for fitting to equipment housing to be carried in ETSI-compliant racks, where the mounting is at the front.
In preferred embodiments a rear mounting is located adjacent the rear edge of the plate. This rear mounting also has a fastener for rigid attachment to the rack, and a rear damping member coupling the rear fastener to the bracket body.
It has been found that conventional ETSI or front-mounted shelves can be damaged by the fact that whereas the support is at the two front side edges, the centre of gravity is towards the centre of the shelf. By providing a further mounting at the rear of each side, the housing is dramatically stabilised during earthquake tests.
In one embodiment to be described below, the rear damping member takes the form of a solid cylinder of elastomeric material, and the bracket body and the fastener are coupled to the opposite faces of the cylinder.
This cylinder is preferably carried with its axis running vertically to absorb vertical vibrations, since the damping member between the front flange and the rack mounting rail will absorb horizontal vibrations.
In another embodiment the rear damping member and the front damping member each take the form of a an annular cylinder, i.e. a substantially cylindrical body of elastomeric material having an axial bore. The fastener, which may be e.g. a bolt, is carried in the bore and the bracket body is mounted on the external surface of the cylinder.
In a particularly preferred embodiment, the fastener is a shoulder bolt having a head, a threaded section, and a shank defining a shoulder between the head and the threaded section, for engagement with a threaded hole in a surface of the rack. The bolt passes through the centre of the bore, and when the bolt is tightened so that the shoulder meets the surface of the rack, the annular cylinder is compressed between the head of the bolt and the rack surface.
Since the damping characteristics of the damping member are determined by its composition, shape, size, and applied forces, this shoulder bolt allows a very precise and repeatable application of a compressive force resulting in a predictable damping vs. frequency response.
The bracket may be anchored to the housing by a hook provided on the bracket body which engages a lip on the housing.
Preferably the bracket body takes the form of a pair of separable body members, each having one of the hooks for engagement with a respective lip on the housing, so that the hooks may be brought into anchoring engagement with the lips by connecting the body members together.
This embodiment is particularly valuable for retrofitting to existing shelves. The bracket can be hooked into place on existing protrusions on the shelf, and the two halves fastened together to secure the bracket. Further securing may then be effected using existing bolt holes, riveting point, etc. to which the conventional mounting bracket was attached. In this way, the bracket of the current invention is more securely fastened than that which it replaces, but there is no necessity to e.g. drill new holes which will change the structural or electromagnetic characteristics of the housing.
A subsidiary bracket may be connected to the bracket of the invention, for mounting an associated equipment housing (e.g. a fan housing) to the rack, so that under vibrational stress the equipment housing and the associated equipment housing move as a single unit. Of course the fan housing or other associated equipment housing may be mounted by means of a bracket according to the invention, and the subsidiary bracket may itself be a bracket according to the invention connected to a main bracket.
The damping member preferably has a vibrational absorption profile which absorbs energies at frequencies of less than about 20 Hz. The natural frequency of the damping member itself, in its uncompressed state is preferably from about 20 Hz to about 60 Hz, more preferably from about 30 Hz to about 40 Hz. When in its compressed state in use, the natural frequency of the damping member is preferably from about 35 Hz to about 45 Hz, most preferably about 40 Hz.
In another aspect the invention provides an equipment housing in the form of a box-like structure having an open front, with a mounting bracket as described above rigidly connected to each side wall of the box.
In another aspect there is provided a rack for mounting equipment housings, the rack having a base, a pair of elongate parallel side members projecting upwards from the base and coupled at their top ends by a top member. Each of the side members has a pair of spaced apart parallel rails extending substantially along the length of the side members, each of the rails having a series of mounting points (such as threaded holes) distributed along its length, whereby each side member may accommodate front and rear sets of fasteners for equipment mounting brackets.
Preferably, where the rack holds equipment housings mounted by a bracket of the present invention, the damping members having a vibrational absorption profile with a maximum response at a frequency approximately equal to a resonant frequency of the rack.
In a further aspect of the invention there is provided a mounting bracket for mounting an equipment housing to a rack, the mounting bracket having a bracket body for rigid attachment to the housing, and a fastener for rigid attachment to the rack, the bracket body having a pair of separable body members, each having a hook for engagement with a respective lip on an equipment housing, such that the hooks may be brought into anchoring engagement with the lips by connecting the body members together.
The invention also provides a method of mounting such a bracket to an equipment housing, the method involving the steps of engaging each of the hooks with a respective lip, and connecting the body members to one another when the hooks are engaged to anchor the bracket to the housing.
The invention further provides a method of mounting an equipment housing to a rack by means of a pair of brackets on opposite sides of the housing, each bracket having a front and a rear fastener, the method involving the steps of placing the housing into the rack between a pair of rack side members such that the front fasteners are in registering alignment with a respective mounting point on a front rack rail of each side member and the rear fasteners are in registering alignment with a respective mounting point on a rear rack rail of each side member, and fastening the fasteners to the mounting points.